Consider the standard 'C' library function malloc:

void *malloc( unsigned int size );

This is perfectly standard ANSI 'C' - nothing Keil-specific here.

As you know, malloc returns a pointer to the area of memory which it has allocated; now, it has no idea whether you want to put chars or ints or arrays or structures or whatever in this area - so it cannot return a char* or int* or any other specific pointer.
It must therefore return as "generic" (or "Abstract" in Keil-speak) pointer which can refer to any arbitrary object

Another example might be where you want to refer to an area of memory either as bytes, or words, or something else. The approaches of using shift-and-mask and unions have recently been discussed, but you could also use a Generic (or "Abstract" in Keil-speak) pointer; eg,

void main( void )
{
void *AbstrPtr; // Abstract pointer

int   Word1 = 0x55AA;
int   Word2;
char  Byte1, Byte2;

	AbstrPtr = &Word1;            // Point to Word1

	Word2 = *(int  *)AbstrPtr;    // Dereference the pointer as an int
	Byte1 = *(char *)AbstrPtr;    // Dereference the pointer as a  byte
	Byte2 = *(char *)(AbstrPtr+1);// ... and access the next byte
}

When dereferencing an Abstract pointer, note that it's necessary to explicitly cast it so that the compiler knows what size object it's dealing with; eg, (int*)